why are my bottle screws chrome bronze ?

[simonfraser]

looking at the recent treads re crevice corrosion, my bottle screws are not shiny ss jobs, but slightly green dull ones. the rest of the standing rigging is ss with norsen terminals.
i suspect the bottle scews are chrome bronze ?? good / bad idea ?

 

[john_morris_uk]

Good idea. Best quality bottle screws are bronze bodies with stainless ends. It prevents the possibility of galling. Galling is when two metals 'weld' themselves together under pressure, and stainless rigging screws can do this very easily if not greased and maintained.

 

[simonfraser]

the slight surface crazing is no problem ?

 

[john_morris_uk]

It depends what you mean by surface crazing. Some bronze bodies are chrome plated. Sometimes the chrome plating starts to fail and you get some strange patterns of corrosion on the surface. The body underneath is still perfectly servicable.

If there was no chrome plating, a good clean (scourer, wire wool?) should remove all the surface rubbish and reveal whether the body is cracked or not. I don't ever remember seeing a cracked bronze bottlescrew body, but its always worth a close look at all fittings.

 

[vyv_cox]

<<< stainless rigging screws can do this very easily if not greased and maintained >>

And even if they are! It is very difficult to guard against galling. Shell used to make a grease specifically for this purpose, it was very heavy and contained an exceptionally high molybdenum disulphide content. However, it then became apparent that MoS2 greases could cause cracking in non-stainless high-tensile bolts, so Shell dropped the product as they were aware that it was used in all sorts of circumstances. It wasn't all that good at preventing galling anyway.

 

[eyehavit]

Just to add,
As I recall, chrome bronze is particularly hard wearing with good low friction characteristics.

 

[simonfraser]

thanks john, i shall give them a gently rub !

 

[Graham_Wright]

I have been recommended Copperslip (and used it so fingers crossed!).

 

[vyv_cox]

I've had lots of success with Copperslip on automotive exhaust pipe bolting but I've never tried it on stainless steel. I can't think of any reason for not using it, so it could be a good solution.

 

[saltwater_gypsy]

The professional stuff is J166 Anti-seize compound made by ROCOL (Leeds, LS268BS). You can get it via RadioSpares (RS) with stock number 691-303. It has a very high copper content and I have used it on bottle screws and undersea applications with complete success. No connection, just pleased to recommend a good product.

 

[PuffTheMagicDragon]

[ QUOTE ]
I've had lots of success with Copperslip on automotive exhaust pipe bolting but I've never tried it on stainless steel. I can't think of any reason for not using it, so it could be a good solution.

[/ QUOTE ]

Is that similar to PBC (poly-butyl-cuprisil ?) ? We used to use that as a lubricant for slow moving machinery parts on ships, especially around steam. I have been using it for years on my bottle screws and elsewhere (even on the Blakes!) and - so far - it has been effective. Could be all in the mind, of course.

 

[charles_reed]

Bronze turnbuckles

are much, much safer than stainless steel.

They don't work-harden, fatigue fail, suffer crevice corrosion.

The green is cupric salts from the bronze which has percolated through the porous chrome plating, which suggests they're more than 7 years old.

 

[simonfraser]

Re: Bronze turnbuckles

thanks charles, i shall go and worry about something else

 

[alec]

I'am sure we are better off with bronze but I never had any problems with stainless at all.

I was persuaded to change to bronze about 4 year's ago and paid top dollar for sta-lok.

The chrome is now coming off and they look terrible ( but probably very safe).

Have to say I would go down the stainless route next time.

Have had terrible problems with ally and stainless mixed together ( rudders etc) and would love to know what we can do about it.

 

[simonfraser]

i'd rather have tatty looking safe ones than shiny dodgy one

 

[wotayottie]

[ QUOTE ]


Have had terrible problems with ally and stainless mixed together ( rudders etc) and would love to know what we can do about it.

[/ QUOTE ]

Not a lot. The problem is that ally oxides occupy more room than the metal used to form them so a stainless screw into ally gets seized up in no time. Insulate with either a plastic as in guard rail sockets of with Duralac or similar but I dont know any real cure.

As already said, stainless has a nasty way of welding up under pressure. To avoid this when producing stainless wire for cold heading into bolts, we used to copper plate it or alternatively coat with soap loaded with moly disulphide. Technology has probably moved on since my day, but stainless threads and bronze bottle screws sounds good to me

 

[FAITIRA]

You have, The bestest. imho. Bill.

 

[ccscott49]

We use a copper thread compound in the oilield for stainless and monel drill collars, that are made up to a torque of 88kft/lbs!! They come apart with no galling or thread damage. Damn good stuff, basically copperslip.
There is also a zinc based one, which is used in the nuclear industry for anti sieze on flange bolts etc. Lots of stainless steel used in this indusytry as in food industry. It can be obtained quite easily, try Brown brothers or similar engineering suppliers.